Impacts of Electrofishing Removals on the Introduced Flathead Catfish Population in the Satilla River, Georgia
Timothy F. Bonvechio, Micheal S. Allen, Dan Gwinn, and Jason S. Mitchell
Abstract.—Recent modeling indicates that increased exploitation on nonnative flathead catfish Pylodictis olivaris may be an avenue for native species recovery. Flathead catfish were illegally introduced into the Satilla River, Georgia, and negative impacts have occurred on native fishes. In an effort to aid in the restoration of native fish on the Satilla River, the Georgia Department of Natural Resources initiated an intensive electrofishing removal effort. In this study, we evaluated the changes in flathead catfish total mortality, condition, and size structure from those efforts. From 2007 to 2009, 13,472 flathead catfish totaling 19,337 kg were removed along a 129-km stretch of the Satilla River. The population size structure changed substantially from containing many large individuals (59% 510 mm total length [TL]) in 2007 to mainly small fish (79% 356 mm TL) by 2009. Total biomass per effort declined from 57.05 kg/h in 2007 to 19.96 kg/h in 2009. Mean individual weight of fish removed decreased from 2.64 kg in 2007 to 1.32 kg in 2008 to 0.61 kg in 2009. Population age structure was also truncated, but there was evidence for higher recruitment and earlier maturation, which would require that intensive harvest be maintained to prevent the population from rebuilding within 2–5 years. Catch-curves revealed increasing total annual mortality rates of 37, 48 and 52%, for 2007–2009, respectively. Considering the life history of the flathead catfish, being a long-lived species that presumably cannot withstand excessive rates of exploitation (i.e., greater than 25% exploitation), our results indicated that an electrofishing removal program is a reasonable management option for areas where this apex predator has been introduced, but continual removal may be required to maintain low biomass.